Page 101 - Enzymes in Tropical Soils

Enzymes in Tropical Soils 89

movement will cease and water molecules will be retained in soils. This water will
be used by plants or eventually vaporized.
As mentioned previously, the soil water will retain heat absorbed by the soil
particles. For a given amount of heat energy, mositened soils will get a slow and
lower increase in temperature that do the dry soils. This phenomenon is caused by
the fact that water possesses high heat capacity, which may slow the heating of
moistened soils. Sunlight energy is the main heat source controlling the soil
temperature.

45
40
GravitationWater
35
Water Content (%) 25 Available Water FC
30

20
15
10 PWP
Unavailable Water
5
0
0 5 10 15 20 25 30 35 40
Clay Content (%)

Fig. 6.4. Soil available water (Salam, 2012).
(FC = Field Capacity; PWP = Permanent Wilting Point; Adapted
from Harpstead et al., 1988).

In addition to soil water content, the amount of energy absorbed by soil
particles depend on several other factors such as soil color, soil cover, topography,
and soil depth. Black soil color absorbs 75% of heat while pale surface absorbs only
25% of the impact heat. The presence of cover vegetation will decrease the soil
heating. Soil surface directly facing the sunlight will heat more quickly than does
the soil surface not directly facing the sunlight. Because heat diffuses through soil
particles, the soil temperature is different, dependent on the soil depth as depicted

Abdul Kadir Salam - 2014